My uncle had a Porsche 924 (well he still has, he just took it too bits and has left it scattered all over garage but that's another story). The engine had been worked on by a previous owner and was in a high state of tune and the car could fly, far faster than it should have been. I borrowed it once and although I didn't measure the fuel consumption it was horrible, probably about 15mpg if driven with mild enthusiasm.
Otherwise, I had a 2l Cortina years ago which was pretty thirsty too but I suppose I was driving with "youthful enthusiasm."